The present invention relates generally to vascular repair devices, and more particularly to intravascular devices which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency and for the delivery of therapeutic agents thereof.
It is well established that various fluid conducting body or corporeal lumens, such as veins and arteries, may deteriorate or suffer trauma so that repair is necessary. For example, various types of aneurysms or other deteriorative diseases may affect the ability of the lumen to conduct fluids and, in turn, may be life threatening. In some cases, the damage to the lumen is repairable only with the use of prosthesis such as an artificial vessel or graft.
For repair of vital lumens such as the aorta, surgical repair is significantly life threatening or subject to significant morbidity. Surgical techniques known in the art involve major surgery in which a graft resembling the natural vessel is spliced into the diseased or obstructed section of the natural vessel. Known procedures include surgically removing the damaged or diseased portion of the vessel and inserting an artificial or donor graft portion inserted and stitched to the ends of the vessel which were created by the removal of the diseased portion. More recently, devices have been developed for treating diseased vasculature through intraluminal repair. Rather than removing the diseased portion of the vasculature, the art has taught bypassing the diseased portion with a prosthesis and implanting the prosthesis within the vasculature. An intra arterial prosthesis of this type has two components: a flexible conduit, the graft, and the expandable framework, the stent (or stents). Such a prosthesis is called an endovascular graft.
It has been found that many abdominal aortic aneurysms extend to the aortic bifurcation. Accordingly, a majority of cases of endovascular aneurysm repair employ a graft having a bifurcated shape with a trunk portion and two limbs, each limb extending into separate branches of vasculature. Currently available bifurcated endovascular grafts fall into two categories. One category of grafts are those in which a preformed graft is inserted whole into the arterial system and manipulated into position about the area to be treated. This is a unibody graft. The other category of endovascular grafts are those in which a graft is assembled in-situ from two or more endovascular graft components. This latter endovascular graft is referred to as a modular endovascular graft.
Intravascular interventional devices such as stents are typically implanted within a vessel in a contracted state, and expanded when in place in the vessel in order to maintain the patency of the vessel to allow fluid flow through the vessel. Stents have a support structure such as a metallic structure to provide the strength required to maintain the patency of the vessel in which it is to be implanted, and are typically provided with an exterior surface coating to provide a biocompatible and/or hemocompatible surface. Since it is often useful to provide localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the stent, it is also desirable to provide intravascular interventional devices, other than stents, with a biocompatible and/or hemocompatible surface coating of a polymeric material with the capability of being loaded with therapeutic agents, to function together with the intravascular devices for placement and release of the therapeutic drugs at a specific intravascular site.
Drug-eluting stent devices have shown great promise in treating coronary artery disease, specifically in terms of reopening and restoring blood flow in arteries stenosed by atherosclerosis. Restenosis rates after using drug-eluting stents during percutaneous intervention are significantly lower compared to bare metal stenting and balloon angioplasty. Restenosis is the normal reaction of the human body to a foreign body being implanted in one of the coronary, carotid, or peripheral arteries. The coating of bare metal stents with an anti-cancer drug is the current approach to decrease or eliminate restenosis. However, current design and fabrication methods for drug-eluting stent devices are not optimal. Accordingly, various limitations exist with respect to such current design and fabrication methods for drug-eluting stents.
One significant limitation, for example, is that current designs for drug-eluting stents fail to provide for uniform drug distribution in the artery. Since uniformity is dictated by metal stent skeletal structure, increasing uniformity by increasing the metal stent surface area makes the stent stiff and compromises flexibility and deliverability. Further limitations include the mixture of the drug in a polymer and/or solvent solution which is then spray coated on the entire stent surface with a primer, drug, and topcoat layers being used to control release kinetics. This approach tends to cause cracking in the drug-coating layer, since the layer also undergoes stretching during stent expansion, and resultant considerable washout of the drug into the blood stream, and only a fraction gets into the tissue/artery. Further, the amount of the drug that can be loaded on the stent is limited by mechanical properties of the coating, since the higher drug content in the polymer makes the coating more brittle and causes cracking thereto. Therefore, loading a higher drug dose requires coating with more polymer on the device. Other limitations in current fabrication methods of drug-eluting stents include the necessity of several coating steps along the length of the stent which is time consuming. As conventional spray coating is capable of programming only one drug release rate kinetics, variation of drug dosing and release kinetics along the length of the stent is not possible using the current coating process.
Several challenges face the major medical device manufacturing companies in regard to implementing a drug-eluting stent into the marketplace. A common method of applying an anti-cancer drug for example, is to first apply a polymer primer layer to the bare metal stent, dissolve the drug into a suitable polymer using a suitable solvent, spray the drug-polymer mixture onto the primer layer, and then apply a polymer topcoat. One particular challenge facing endovascular graft medical device manufacturers is providing a drug elusive device having a flexible graft covering the drug-polymer layered expandable stent. Medical device manufacturing companies are also faced with the challenge of making drug-eluting devices that have adequate drug storage capability. The creation of channels and/or depots into tubing using laser machining is one approach that has been considered to resolve this issue. However, it has been found that laser machining requires more control (i.e., consistency) in order to be a reliable and controlled manufacturing process. For example, in forming depots using laser machining, the depth thereof is not precisely repeatable from one depot to the next. Further, studies have shown that the use of laser machining in creating channels and/or depots into tubing is not a cost effective way to manufacture high volumes of components with intricate geometric shapes and designs at a competitive price.
What has been needed and heretofore unavailable in the art is a method of manufacturing endovascular grafts for the subsequent manufacture into drug-eluting devices that would increase the reservoir capacity of the device by incorporating longitudinal and/or circumferential channels and geometrically-shaped depots into the endovascular graft structure. Thus, it would be desirable to have a drug-eluting device that is optimally designed to have increased drug storage capability, which improves the reproducibility of drug storage features currently being manufactured. The present invention meets these and other needs.